1. Field of the Invention
The invention relates to the papermaking art and, in particular, to the manufacture of paper and paperboard which exhibit improved water resistance properties. This invention also relates to articles of manufacture made from such products such as file folders, non-corrugated containers, and the like.
2. Background of the Invention
Heavy weight cellulosic paper and paperboard webs and products made from same such as file folders and paperboard file containers are often subject to liquid or water damage during routine handling and long term storage. If moisture or aqueous liquid are absorbed by the paper or paperboard materials, the materials may become soggy, warped and/or weakened thereby reducing their usefulness and potentially allowing the liquids to contact and damage documents which may be stored in containers made with the paper or paperboard materials.
Surface sizing, i.e., the addition of sizing agents to the surface of a paper sheet that has been at least partially dried, is widely practiced in the paper industry, particularly for printing grades to improved water holdout (sizing). The most widely used surface sizing agent is starch. However, starch sizing alone has not been effective in providing water resistance to paper and paperboard products.
Accordingly, there exists a need for improved cellulose-based products, and in particular relatively heavy weight paper and paperboard products, which exhibit improved resistance to water and to a process for the manufacture of such water resistant cellulose-based products.